This present invention refers to a process to make a plastic material and more precisely to a process for thermally manufacturing synthetic paper, a fastening strip made with this material and this process, a fastening device that uses the manufactured strip and to products to fasten sheets, previously perforated, that use this fastening device.
Document WO2009/134764 of Medoff is presented, which refers to methods for producing cellulosic materials to be used to manufacture paper that include treating dry cellulosic or lingo cellulosic raw materials having a first average molecular weight with ionizing radiation and controlling such radiation. Even though it refers to a process for producing cellulosic material, it does not refer to a process to modify the shape of a sheet of synthetic paper.
Also presented is Mexican document MX2006JL00043, which refers to a thermal forming device to produce items from a pre-form of natural fibers combined with a thermo-plastic which is characterized because it covers an innovative thermal system based on specially designed electric resistances that allow a more efficient use of the energy resources used in the process. The thermal system consists of electric resistances each one having the energy distributors placed in the compression sheets of the thermal forming device, rods that couple with the distributors and are inserted into the mold until reaching a depth close to the molding surface and connectors that establish electrical coupling among the distributors and its associated rods to deliver electric energy that turns into heat only to those areas in which heating is required for the thermo-forming process. None of the elements described here mentions or suggests that it is a process for thermo-forming synthetic paper, in sheets.
WO/2008/063619 of BURNS refers to structures of molded polymers including pipes, plates, cards, bottles, etc. that are formed with silicon-doped nanoparticles over, with or in the polymer matrix. This invention is not related with nanoparticles.
We respectfully submit that these are the documents known to the inventors and that they are related in some way to the field of synthetic paper molding by thermoforming.
According to the above mentioned, it is believed that there is no existing process for thermo-forming synthetic paper and that also resembles in anyway to what is described here.
Regarding the fastener device, the closest prior art is in document WO/2009/MX/00021, which is an application presented by the same applicant of this invention. In this PCT application, a device with a configuration similar to the here described device is disclosed; however, there are important differences that, contrary to what is expected, improve in an important way the functioning of the device. It should be noted that this document neither describe or mention a method or process for thermo-forming synthetic paper, nor devices or products made using the device mentioned in this document.
Documents U.S. Pat. No. 4,867,594, U.S. Pat. No. 4,157,152, GB191024895, U.S. Pat. No. 3,016,224, DE29807829 and U.S. Pat. No. 2,925,239, also Spaniard patent 2108573 are known in the prior art. None of these documents describe a device that holds sheets like the present device does. The devices shown are not used to manufacture elements like calendars, recipe books, sheet dispensers or information cards, catalogs, phone books, etc.
The device described in document WO/2009/MX/00021 has some inconveniences now overcome by the object of the present invention. One of those inconveniences is that during operation, sheets get stuck when they are lifted, causing arrangement problems of the sheets already seen or used and even damage to the sheets. Another inconvenience is that the placement of the device on its base prevented its application to other articles such as calendars, information cards dispensers or similar elements. A second base was needed so the tab in the device could be kept in place and to keep it in position since it has a much smaller moving space.
To prevent sheets from getting stuck, it was envisioned to increase the diameter of the curved part of the device. This increase in the diameter of the ring, curved part or fastening hook, which appears simple, was not simple to implement because the manufacturing process did not allow obtaining the ring with the desired characteristics as will be shown later and thus it was necessary to carryout important analyses in order to find other materials not having the problems described below. This search was unsuccessful and given this failure, it was searched and the manufacturing process of the fastener built based on synthetic paper could be modified, in order to obtain the desired properties.
The process had to be modified since the desired product had two inconveniences when formed by matching molding: a) a burr that decreased elasticity properties indispensable for the correct functioning of the device and b) its impossibility to be used in the manufacturing of a device with a larger diameter and smaller caliber. Therefore, a manufacturing process had to be searched that on the first hand did not leave a burr and secondly, was able to produce a piece with a smaller caliber and a larger diameter without losing its elastic properties to recover the semi-circular shape when a deforming force is applied.
The process found belongs to the type of forming techniques with heating or thermoforming. Among these techniques we find the following:                Forming by adaptation, in which a hot sheet is placed over the male mold or is raised to the mold in order to adapt to its shape. Adaptation process is completed by creating a vacuum between the male mold and the sheet, or applying air pressure to it. Products made by this process show a large thickness on the bottom that decreases until it reaches a minimum at the edges, which is not convenient for the purposes of the piece and processes described here.        Vacuum Molding, where the sheet is fixed on the edge of the female mold and then a vacuum is created. In contrast with the preceding process, the thickness of the piece is larger at the edges and reaches a minimum on the inferior part.        Pressure Forming, which is similar to vacuum molding, and compressed air up to a certain pressure is applied on the sheet, thus the system requires a chamber. This procedure is used to form thin sheets of materials such as PP, which is supplied in rolls, or to transform large thickness sheets in pieces with a fine detail surface.        Free blowing. Compressed air is applied between a chamber that substitutes the mold, nonexistent in this case, and the sheet to obtain a bubble with a height controlled by means of a photocell. Since the bubble formed from the sheet does not touch any metallic element, it has no marks and, except in the proximity of the fastening frame, has a regular thickness. Air cools the bubble making the piece rigid. The system is extensively used in “blister” containers (which means exactly “ampule”) from a thin sheet supplied in rolls.        Mold and counter mold, to form pieces from relatively rigid polymers, such as PS foam. Vacuum can be applied to the female mold to aid in the forming process. Even though the closing pressures are about 0.35 MPa, certain movement of the material could be produced if forces of 1 MPa are applied.        Multiple stage forming, technique that was developed since the previously described methods have the difficulty of controlling the thickness in complex pieces such as parts with reduced radius and deep indents, especially when plates with an important thickness are formed. That is why methods with more than one step have been created, being the first one a type of stretching the sheet.        